You're conflating "solved" with "boring" and missing the actual point. Boring means predictable failure modes and a massive community that's already hit your edge cases. Postgres has 30 years of operational know-how documented. Your Lambda/DynamoDB stack? Sure, less ops overhead, but you're trading that for vendor lock-in and cold starts that bite you at 3am.
Both are valid. Neither is objectively boring. But pretending AWS managed services eliminate ops work is naive. You just swapped database migrations for wrestling with DynamoDB's LSI limits and Lambda's concurrent execution model.